UrbanPro
true

Take BSc Tuition from the Best Tutors

  • Affordable fees
  • 1-1 or Group class
  • Flexible Timings
  • Verified Tutors

Search in

Non Homologous End Joining Recombination

S
Sneha R.
25/05/2017 0 0

Non-homologous end joining (NHEJ) functions in all kinds of cells, from bacteria to man, and is involved in many different processes, such as DNA repair, telomere maintenance, and the insertion into the genome of HIV-1 and repetitive sequences. NHEJ of double-stranded breaks (DSBs) in DNA is accomplished by a series of proteins that work together to carry out the synapsis, preparation and ligation of the broken DNA ends. The main proteins involved in NHEJ in eukaryotes are DNA ligase IV, XRCC4, the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), Ku protein, and possibly Artemis. Deficiencies in any one of these proteins results in hypersensitivity to DNA DSB-inducing agents, such as ionising radiation.

Three steps have been identified in the NHEJ process: DNA end-binding and bridging, terminal end processing, and ligation:

(i) DNA End-binding and Bridging:

NHEJ is initiated by the recognition and binding of the Ku protein to the broken DNA ends, Ku is a heterodimer of Ku70 and Ku80 that forms the DNA-binding component of DNA-dependent protein kinase (DNA-PK). Ku forms a ring that encircles duplex DNA, cradling two full turns of the DNA molecule. By forming a bridge between the broken DNA ends, Ku acts to structurally support and align the DNA ends, to protect them from degradation, and to prevent promiscuous binding to unbroken DNA. Ku effectively aligns the DNA, while still allowing access of polymerases, nucleases and ligases to the broken DNA ends to promote end joining. 

Once Ku is in place, it recruits the catalytic subunit of DNA-PK, namely DNA-PKcs, which is a serine/threonine kinase in the phosphoinositide 3-kinase (PI3K) family that is believed to be a signalling molecule in response to cellular stress.  DNA-PKcs can phosphorylate several nuclear proteins in vitro, including DNA ligase IV and XRCC4. The phosphorylation of DNA ligase IV and/or XRCC4 may affect their interactions with Ku and other proteins. 

 (ii) Terminal End Processing:

NHEJ requires two DNA blunt ends in order to join them together. In some cases, terminal processing of the DNA ends is required before ligation can occur. For instance, a single-stranded overhang requires DNA synthesis by a polymerase to fill-in gaps, which creates blunt ends that can be ligated. Alternatively, single-stranded overhangs can be trimmed off via nuclease activity, a role that may involve the Artemis protein, which belongs to the metallo-beta-lactamase family (IPR011084). DNA-PKcs phosphorylates and binds to the Artemis protein, and the resulting Artemis/DNA-PKcs complex is thought to have nuclease activity that cleaves 5’ and 3’ DNA overhangs.

 (iii) Ligation:

Once the blunt ends are in place, the XRCC4/DNA ligase IV ligation complex is recruited to join the DNA ends together. DNA ligase IV carries out the ligation step, but it requires the binding of XRCC4 to do so. XRCC4 functions as a regulatory element to stabilise DNA ligase IV, to stimulate ligase activity, and to direct the ligase to the site of DNA breaks via its recognition helix and DNA-binding capacity. 

 

 

0 Dislike
Follow 0

Please Enter a comment

Submit

Other Lessons for You

7 -WAYS THAT CAN IMPROVE THE LIFE OF A STUDENT
1. Classroom attentionSometimes #students loose their concentration in to the #classroom and not grasp the topic properly and hence loose their interest in to subject (s). As a result bad score bad performance....
D

Dr

1 0
0

Visualize the concepts and they will be better understood.
Imagine and create your own visuals in mind, believe me that it'll help you relate and remember the concepts much well.For example, I understood the concept of Crests and...

SINCERITY TOWARDS OURSELVES
Please see that we are sincere to ourseleves....see that we prepare a small schedule which is convenient and implementable by us..At the end of a week atleast, check if we are able to fulfill it and try...

Textile water waste treatment
extile wastewater purification: The textile industry is rated as one of the most polluting and chemically intensive industrial sectors (Uzal, 2015). -Chemicals like acids, alkalis, colours, high BOD/COD...

Easy ways to remember Periodic Table
You can easily remember the Periodic table by remembering some Hindi Mnemonics Group 1 is known as alkali metals. It includes Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Ru), Caesium (Cs), and...
X

Looking for BSc Tuition Classes?

The best tutors for BSc Tuition Classes are on UrbanPro

  • Select the best Tutor
  • Book & Attend a Free Demo
  • Pay and start Learning

Take BSc Tuition with the Best Tutors

The best Tutors for BSc Tuition Classes are on UrbanPro

This website uses cookies

We use cookies to improve user experience. Choose what cookies you allow us to use. You can read more about our Cookie Policy in our Privacy Policy

Accept All
Decline All

UrbanPro.com is India's largest network of most trusted tutors and institutes. Over 55 lakh students rely on UrbanPro.com, to fulfill their learning requirements across 1,000+ categories. Using UrbanPro.com, parents, and students can compare multiple Tutors and Institutes and choose the one that best suits their requirements. More than 7.5 lakh verified Tutors and Institutes are helping millions of students every day and growing their tutoring business on UrbanPro.com. Whether you are looking for a tutor to learn mathematics, a German language trainer to brush up your German language skills or an institute to upgrade your IT skills, we have got the best selection of Tutors and Training Institutes for you. Read more